1. Field of the Invention
The present invention relates to a construction method of a foundation for an underwater support structure, and more particularly, to a construction method of a foundation for an underwater support structure, which is capable of rapidly installing the foundation of a large-scale structure, such as an offshore wind generator, on a sea floor, and being easily inserted and constructed into a pile while sufficiently securing a horizontal load supporting capability.
2. Discussion of Related Art
In a wind generator which produces electric power using wind, a blade is installed at a rotational shaft of the wind generator, and configured to produce the electric power using a rotational force generated as the blade is rotated by the wind.
The wind generator is an apparatus which converts wind energy into electric energy, and generally includes the blade, a transmission, and a generator.
Here, the blade is a device which is rotated by the wind and converts the wind energy into mechanical energy. The transmission is a device in which the rotational force generated at the blade is transmitted to a gearbox via a central rotational shaft to have increased revolutions per minute (RPM) required in the generator and then to rotate the generator. The generator is a device which converts the mechanical energy generated at the blade into the electric energy.
Since such a wind generation system has a simple structure, is easily installed, and thus easily managed and maintained, and also may realize an unmanned and automated operation, an introduction thereof is being rapidly increased.
In the past, wind generation structures were mainly installed on land. However, a large-scale wind generation farm has been recently constructed on the sea due to problems of wind resource potential, aesthetic of the view, location restriction, or the like.
However, in order to stably construct the wind generation structures on the sea, a stable installation method for the blade, the transmission, and the generator which are installed at a high position is required.
The offshore wind generation structure may be divided into a turbine and a foundation. At this time, the same technology as that of a land wind turbine is basically applied to the offshore turbine.
The foundation may be divided and described as representative two types.
Firstly, a monopile type is the most commonly used foundation method for an offshore wind generation farm, and may be installed at a depth of 25 to 30 m. When the monopile type is used in the large-scale wind generation farm in a manner in which a large diameter pipe is fixed in a sea floor through driving or drilling, economic efficiency is enhanced. At this time, a foundation diameter of the monopile type is about 3 to 3.5 m.
Secondly, a jacket type is a foundation method which is drawing keen attention from many countries with the offshore wind generation farm, has been verified through testing and may be installed at a depth of 20 to 80 m, and also which is supported by a jacket type structure and fixed in the sea floor by a stake or a pile. The jacket type which is a deep sea depth structure is actually used in many places, and thus has high reliability. Like the monopile type, when the jacket type is used in the large-scale wind generation farm, the economic efficiency is enhanced.
FIG. 1A is a view illustrating an offshore wind generation structure with a monopile foundation and a steel tower as a support structure according to conventional technology.
Referring to FIG. 1A, the offshore wind generation structure with the monopile foundation and the steel tower according to the conventional technology largely includes a foundation and a support structure, and more specifically, may include a tower 10, a nacelle 20, a blade 30, a monopile 40 and a transition piece 50.
Further, a pitch system, a hub, a main shaft, a gear box, a high speed shaft, a generator, a yaw system, and so on are provided at the nacelle 20 installed an upper portion of the tower 10.
The tower 10 is formed of a steel pipe having a thickness of 25 to 40 mm, as illustrated in a cross sectional view taken along a line A-A.
Therefore, it may be understood that the foundation should be fabricated and constructed as a structure for resisting a large self-load and an applied load. Particularly, in the case in which the foundation is installed at the sea floor, the economic efficiency according to the fabricating and constructing methods thereof should be sufficiently ensured, and particularly, workability and constructability are very important factors in compression of a construction period.
FIG. 1B illustrates a construction example of the conventional foundation.
A concrete structure fabricated in a precast manner is used for the foundation. A leg part 61 is formed at a lower portion of the tower, and a bucket part 62 is provided at an end of the leg part 61 to be supported on the sea floor.
At this time, a hole for pile construction is previously formed at the bucket part 62, such that a boring hole is formed in the sea floor through the hole using a boring machine 63 such as an auger.
Then, after removing the boring machine, a pile (not shown) is inserted and installed in the boring hole, and a grouting preparation 64 is pressurized and injected into the hole so that the pile is integrally formed with the foundation to disperse and support the load.
However, when such a method is used, there are some problems in that the boring machine 63 is used at the sea floor, and the method may not effectively respond to an extraction force generated when the pile is constructed. Therefore, a more effective construction method is required in the construction of the foundation for a large-scale structure such as the offshore wind generator.